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A relationship between Arctic sea ice melt and melting glaciers?

Last summer, a chunk of ice three times the size of Manhattan broke off Petermann Glacier in Greenland and floated out to sea. The calving left miles of newly open water in the deep Petermann Fjord, which had been capped in a thick layer of glacial ice. New research out this summer confirmed that it was likely the largest calving in the region since observations began in 1876. What does this event tell us about climate change in the Arctic?

Scientists say it is clear that Greenland is losing ice. Jason Box, a climatologist at Byrd Polar Research Center, has closely studied the Petermann Glacier, as well as the climate and ice of Greenland as a whole. He said, "Petermann is not the only loser in Greenland. In fact, there is a very clear pattern of glacier area loss all around the island, one that has increased in the past decade."

But scientists cannot pin the Petermann glacier event -- or any specific ice breakup -- squarely on climate change. There are too many variables that determine exactly when a glacier calves. Box said, "A single cracking event could conceivably be triggered by a seagull, acting like the straw that broke the camel's back." Data compiled by Box show that air temperatures in Greenland have risen sharply in the last 25 years. The extent of melting and ice retreat has accordingly increased.

Glaciers and sea ice

What do changes in the Greenland Ice Sheet have to do with declining sea ice in the Arctic? Studies show that the ice on land and ice in the ocean are intimately related. The decline in sea ice could speed up ice loss in Greenland. "It is reasonable to speculate that changes in sea ice duration and concentration in the vicinity of glacier fronts should impact their stability," said Box. "As the sea ice melts, the ocean can be stirred up more by strong Arctic winds and change fjord water circulation and the sub-marine melt regime." Winter sea ice also acts as a buttress against glacier ice flow, seasonally slowing the flow speed. An earlier break-up and later freeze-up of sea ice in the fjords may play a role in the ice sheets' mass balance.

The difference between Greenland's ice and sea ice is that the sea ice floating on the Arctic Ocean does not contribute to sea level rise, just as a melting ice cube in a glass of water will not cause the water level to rise. But the miles of ice that cover Greenland are different: if that ice melts, it would be like adding more ice cubes to that glass of water.

Measurements show that Greenland's ice does indeed flow into the ocean faster than snow accumulates on the island. This means that sea level is rising -- a potential problem for people around the world. "As ice sheets continue to contribute to sea level rise, as expected in climate warming scenarios, the effects will be felt not just in coastal areas," Box said, "The effects will also be felt globally, where the coastal impacts lead to economic ripple effects."

For more details and photos of the Petermann Glacier, before and after the 2010 calving, visit Jason Box's Web site.

This article originally appeared on Icelights, a blog published by The National Snow and Ice Data Center. It is reprinted here with permission.